Solar cells having a transparent composition-graded buffer layer

Abstract

A solar cell includes a first layer having a first-layer lattice parameter, a second layer having a second-layer lattice parameter different from the first-layer lattice parameter, wherein the second layer includes a photoactive second-layer material; and a third layer having a third-layer lattice parameter different from the second-layer lattice parameter, wherein the third layer includes a photoactive third-layer material. A transparent buffer layer extends between and contacts the second layer and the third layer and has a buffer-layer lattice parameter that varies with increasing distance from the second layer toward the third layer, so as to lattice match to the second layer and to the third layer. There may be additional subcell layers and buffer layers in the solar cell.

Description

[0001] This invention was made with Government support under Contract No. F29601-98-2-0207 awarded by the United States Air Force. The Government has certain rights in this invention.[0002] The present invention generally relates to semiconductor materials and, more specifically, to solar cells. BACKGROUND OF THE INVENTION [0003] A solar cell is a photovoltaic (PV) device having one or more photovoltaic junctions. Each junction is formed by a photovoltaic semiconductor layer. At each junction, incident light energy, and specifically solar energy, is converted to electrical energy through the photovoltaic effect. [0004] The interest in solar cells has been increasing due to concerns regarding pollution and limited available resources. This interest has been for both terrestrial and non-terrestrial applications. In space applications, the use of nuclear or battery power greatly increases a spacecraft's payload for a given amount of required power to operate the satellite. Increasing t...

AI Technical Summary

Benefits of technology

The present invention provides an improved solar cell that offers increased efficiency and performance with little change in cost. The solar cell includes a first layer, a second layer, and a third layer, wherein the second layer includes a photoactive material. The first and second layers have different lattice parameters, which are accommodated by a graded buffer layer that increases or decreases the lattice parameter with increasing distance from the first layer. The use of the graded buffer layer achieves the desired lattice matching and epitaxial relationship through the thickness of the solar cell, minimizing internal stresses and strains, and for good electron movement through the thickness of the solar cell. The result is improved performance of the individual subcells and the solar cell.

Problems solved by technology

A limitation in the existing 4J, 5J, and 6J devices (and cells with even more junctions) is the requirement of nearly perfect lattice matching of the inserted subcell and the underlying and overlying materials.

Any substantial deviation, such as more than about + / −0.1 percent difference, in lattice parameter without proper design to incorporate the change in lattice parameter will result in degradation of the overall efficiency of the solar cell.

Another limitation is the reliance on the GaInAsN alloy lattice-matched to the GaAs or Ge layers.

The lattice-matched GaInAsN material has poor quality when produced by available techniques.

The problem results from the need to incorporate a large amount of nitrogen to achieve the 1.0 eV band gap and the lattice-matched condition simultaneously.

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